1. Field of the Invention
This invention relates to solvent-resistant polymer mixtures that can be processed thermoplastically, containing of mixtures of polymethyl, ethyl, or propyl acrylate, polyvinyl acetate, or polyvinyl propionate, grafted to a chemically crosslinked elastomer with a glass transition temperature &lt;0.degree. C., and polyvinylidene fluoride.
2. Discussion of the Background
The compatibility of polymethyl methacrylate and polyethyl methacrylate with polyvinylidene fluoride (PVDF) in mixtures has been known for a long time. (See S. Noland et al., Polym. Prepr. Amer. Chem. Soc., Div. Polym. Chem. 11, 355 (1970); U.S. Pat. No. 3,253,060). Such mixtures satisfy the criterion of a single glass transition temperature Tg between that of the polymer components, and they also show complete transparency over a broad range of mixtures.
Polyvinylidene fluoride (PVDF) has also been found to be compatible with a large number of different polyvinyl compounds. Thus, mixtures of PVDF with polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polyvinyl acetate, and polyvinyl methyl ketone were described by D. R. Paul et al. (D. R. Paul et al., Polymer Engineering and Science, 18, No. 16, 1225-1234 (1978)). Compatible mixtures of polymethyl methacrylate with copolymers of vinylidene fluoride and hexafluoroacetone are described by S. Miyata et al. and Maeda et al. (S. Miyata et al., Polym. Propr. Jpn. 34, 1074 (1985), and Maeda et al., U.S. Pat. No. 4,617,350 (1986)). The miscibility of polyvinylidene fluoridehexafluoroacetone copolymers and ethylene-vinyl acetate copolymers is described by Hasegawa (Masatoshi Hasegawa and Saburo Akiyama, Polymer Journal, 20, 471-476 (1988)).
The crystallization behavior of PVDF-PMMA blends is described by various authors (Wendorff et al., Makromol. Chem., Rapid Commun. 7, 591-597 (1986), B. R. Hahn et al., Polymer 28, 201-208 (1987), and J. L. Halary et al., Macromolecules 21, 2988-2994 (1988)).
It has been found empirically that the tendency of PVDF to crystallize decreases clearly when PMMA is added (T. Nishi, T. T. Wang, Macromolecules 8, 909 (1975)). It is assumed that crystalline PVDF dissolves in the amorphous polymethacrylate melt and that the PVDF, now amorphous, acts as a plasticizer for the glassy polymethacrylates (See S. Noland et al. in N. A. Platzer, Multicomponent Polymer Systems, Advances in Chemistry Series 99, American Chemical Society 1971).
Thus, PVDF can be added in rather small proportions to polymethyl methacrylate (PMMA) as a polymeric elasticizer (See U.S. Pat. No. 3,458,391), while conversely, PMMA can be added to PVDF in small amounts as a processing aid (U.S. Pat. No. 3,253,060). Experience shows that no distinct improvement of properties of PMMA is achieved by adding about 2-20 wt. % PVDF to PMMA.
It is possible to obtain blends with improved properties, particularly improved mechanical and optical properties, improved processability, and improved stability by mixing compatible polymers, and blends have already led to a number of commercially successful products (See H. F. Mark et al., Encyclopedia of Polymer Science & Engineering, 2nd Ed., Vol. 12, pp. 399-461, J. Wiley & Sons, New York 1988).
Efforts to utilize the known miscibility between PMMA and PEMA as representatives of acrylate polymers on the one hand, and PVDF on the other, to produce technically advanced products, has so far been less successful. Further, it is desirable to partially substitute a more economical polymeric component for the relatively expensive PVDF by blending, if possible without impairing the favorable properties attributed to PVDF.